On Thu, Dec 08, 2005 at 07:50:15AM -0800, Tom Williams wrote:

A friend of mine took a bunch of photos using her Vivitar 3.2MP digital camera with the camera set at 640x480 resolution. She wanted 4x6 prints of those and printed a bunch that came out looking all pixelated and basically like crap. Since then, we've set her camera back to the max resolution since previous photos taken at this resolution printed fine as prints.

My question: is there anyway to use Gimp to scale the 640x480 images so they look as best as possible (no pixelation if possible) as 4x6 prints? I've scaled the images to 4"x6" and have increased pixels per inch and have run many filters with no real success. Or is my friend basically stuck with what she has?

they probably use just about the same algorithms for scaling as gimp does. it is a little like asking if "if i look at this clock instead of the one i have, will i get 4 extra hours in my day". i am not sure if it is the best metaphor, but it is close.

there might be some that can be fixed after the rescaling with perhaps some of the sharpening tools or other things i haven't though of yet but mostly the answer is no.

sorry.

carol

Tom Williams wrote:

A friend of mine took a bunch of photos using her Vivitar 3.2MP digital camera with the camera set at 640x480 resolution. She wanted 4x6 prints of those and printed a bunch that came out looking all pixelated and basically like crap. Since then, we've set her camera back to the max resolution since previous photos taken at this resolution printed fine as prints.

My question: is there anyway to use Gimp to scale the 640x480 images so they look as best as possible (no pixelation if possible) as 4x6 prints? I've scaled the images to 4"x6" and have increased pixels per inch and have run many filters with no real success. Or is my friend basically stuck with what she has?

You can resize the image up in "steps" to smooth out the pixelization and rough edges as you resize it, but you will never regain the missing detail that was not recorded when the photo was taken at such a low resolution so the resulting image will be soft. (Sharpening will help some, but not a lot.)

To upsize in steps, increase the image size by no more than 10% (some say no more than 5%) at a time until it is at the desired size. For minimum quality 4x6 print you want 150 dpi which means you need 600x900 pixels (her 480x640 will need to be cropped as it is the wrong proportion for a 4x6, which means you need to resize it larger, then crop), for better quality you want 300 dpi which means 1200x1800 pixels. Upsizing in 5% increments takes 22 steps to get to ~1200x1800:

480 640 1 504 672
2 529 706
3 556 741
4 583 778
5 613 817
6 643 858
7 675 901
8 709 946
9 745 993
10 782 1042
11 821 1095
12 862 1149
13 905 1207
14 950 1267
15 998 1331
16 1048 1397
17 1100 1467
18 1155 1540
19 1213 1617
20 1274 1698
21 1337 1783
22 1404 1872

Upsizing in 10% increments takes 11 steps:

480 640 1 528 704
2 581 774
3 639 852
4 703 937
5 773 1031
6 850 1134
7 935 1247
8 1029 1372
9 1132 1509
10 1245 1660
11 1369 1826

10% goes faster, but only you can tell if the slower method will produce an improved result on this particular image.

I'm not presently using gimp (I gave up and returned to photoshop and am mostly lurking to see if using gimp is something I should try again in the future), so I can't tell you the exact method for resizing but I hope that this is something you already know how to do.

jc

On 12/8/05, Tom Williams wrote:

My question: is there anyway to use Gimp to scale the 640x480 images so they look as best as possible (no pixelation if possible) as 4x6 prints?

You can look at
http://www.greyc.ensicaen.fr/~dtschump/greycstoration/index.html and use that program for resizing. An impressive demonstration of the power of this algorithm can be found at http://www.greyc.ensicaen.fr/~dtschump/greycstoration/demo.html

btw, is there anyone working on a gimp plugin for this?

My question: is there anyway to use Gimp to scale the 640x480 images so they look as best as possible (no pixelation if possible) as 4x6 prints?

4x6 at 600 dpi is 2400x3600 pixels, and you have 640x480. It is theoretically impossible to get the extra detail from this. In practice there may be an in-betweening, morphing or anti-aliasing algorithm that can get you part way. But it can't give you the detail that was never captured, and is bound to produce a blurred result. You need an artist to fill in the details!

Consider reducing your picture to 320x240, then 160x120, then 80x60 and onwards to 8x6 and 4x3, i.e. 12 pixels. Or even onwards to two pixels, then one.

Now send me the one pixel and ask me to reverse the process. Could I reproduce for you your nice 640x480 graphic?

JC Dill writes:

You can resize the image up in "steps" to smooth out the pixelization and rough edges as you resize it, but you will never regain the missing detail that was not recorded when the photo was taken at such a low resolution so the resulting image will be soft. (Sharpening will help

Someone asked me recently about scaling up cartoon images (e.g. to turn a small carton image into desktop wallpaper) and had the impression that something like this might work. But I wasn't able to find any information on these techniques on the web.

For a cartoon, you start with sharp edges and fairly even colors, so the problems aren't the same as with digital photos. Although you can't get more information than was present in the small image, are there techniques that let you scale up while preserving edges, so for instance a thin sharp black line becomes a thick sharp black line rather than a thick blurry grey line? Scaling up in steps didn't seem to make much difference. I thought perhaps indexing to a small number of colors might help, but I still got too many greys on the edges of the blacks. By playing with Levels I was able to sharpen up the scaled images somewhat, but I wonder if there are better ways. Any tips?

...Akkana

On Fri, Dec 09, 2005 at 11:41:28AM -0800, Akkana Peck wrote:

Someone asked me recently about scaling up cartoon images (e.g. to turn a small carton image into desktop wallpaper) and had the impression that something like this might work. But I wasn't able to find any information on these techniques on the web.

With low color images (comics, game counters, etc), I have better luck with converting the image to an SVG (Gimp Path), then scaling the path to the new size. GIMP and Inkscape both have tracing utilites to get you started on the path. Inkscape's is better, but they both can work with the right constraints.

Jeff

Akkana Peck wrote:

For a cartoon, you start with sharp edges and fairly even colors, so the problems aren't the same as with digital photos. Although you can't get more information than was present in the small image, are there techniques that let you scale up while preserving edges, so for instance a thin sharp black line becomes a thick sharp black line rather than a thick blurry grey line? Scaling up in steps didn't seem to make much difference. I thought perhaps indexing to a small number of colors might help, but I still got too many greys on the edges of the blacks. By playing with Levels I was able to sharpen up the scaled images somewhat, but I wonder if there are better ways. Any tips?

Try a series where you scale up a small amount (5-10%) and then use unsharp mask to crisp up the edge after each upsize iteration. It will probably take some playing around to get the right mix of sharpening.

Good luck!

jc

Steve Stavropoulos wrote:

On 12/8/05, Tom Williams wrote:

My question: is there anyway to use Gimp to scale the 640x480 images so they look as best as possible (no pixelation if possible) as 4x6 prints?

You can look at
http://www.greyc.ensicaen.fr/~dtschump/greycstoration/index.html and use that program for resizing. An impressive demonstration of the power of this algorithm can be found at http://www.greyc.ensicaen.fr/~dtschump/greycstoration/demo.html

btw, is there anyone working on a gimp plugin for this?

Have a look at your first link - it works great here.